Conventionally, such a fuel cell system is known as is provided with a fuel cell where a fuel gas (for example, hydrogen) is supplied to a fuel electrode and an oxidant gas (for example, air) is supplied to an oxidant electrode to thereby make an electrochemical reaction of these gases, thus implementing a power generation.
With respect to the fuel cell system of the above type, nitrogen included in the air is permeated to the fuel electrode side, so that the fuel electrode has a portion having a high nitrogen concentration, that is, a portion having a low hydrogen concentration. The thus caused gas unevenness is a cause for deteriorating members included in the fuel cell. Then, Patent Literature 1 discloses a method of changing gas pressures of the fuel electrode and oxidant electrode to thereby purge the water of the fuel cell and the accumulated unreactive gas.